题目：

题解：

class Solution {Random rand;List<Integer> arr;int[][] rects;public Solution(int[][] rects) {rand = new Random();arr = new ArrayList<Integer>();arr.add(0);this.rects = rects;for (int[] rect : rects) {int a = rect[0], b = rect[1], x = rect[2], y = rect[3];arr.add(arr.get(arr.size() - 1) + (x - a + 1) * (y - b + 1));}}public int[] pick() {int k = rand.nextInt(arr.get(arr.size() - 1));int rectIndex = binarySearch(arr, k + 1) - 1;k -= arr.get(rectIndex);int[] rect = rects[rectIndex];int a = rect[0], b = rect[1], y = rect[3];int col = y - b + 1;int da = k / col;int db = k - col * da;return new int[]{a + da, b + db};}private int binarySearch(List<Integer> arr, int target) {int low = 0, high = arr.size() - 1;while (low <= high) {int mid = (high - low) / 2 + low;int num = arr.get(mid);if (num == target) {return mid;} else if (num > target) {high = mid - 1;} else {low = mid + 1;}}return low;}
}